2007.5-2010 GMC Duramax LMM Engine Parts

What GM changed when the LMM arrived in the Sierra HD

Mid-2007 the heavy-duty Sierra moved to the new body, and a new engine came with it. Compared with the LBZ it replaced, the LMM added a diesel oxidation catalyst and a diesel particulate filter, closed crankcase ventilation that routes blow-by back to the intake, more cooling capacity, a more efficient variable-geometry turbo and a low-ash CJ-4 oil requirement. The long block it inherited is the strong one: reinforced block casting, upgraded main bearing material, thicker connecting rod I-sections and a larger piston pin bore, cast aluminum heads on a gray iron deep-skirt block, a nitrided forged crankshaft and fracture-split forged rods. Bore and stroke are 4.055 in by 3.897 in at 16.8:1 compression. It is a cam-in-block overhead-valve Duramax with hydraulic roller lifters and four valves per cylinder, fires 1-2-7-8-4-5-6-3, and weighs about 835 lb. Fuel is Bosch common rail at up to 26,000 psi through six-hole nozzles, the sump holds 10 quarts with the filter, and a warm engine idles near 680 rpm.

What fails and why

Start with the soot. The EGR valve and cooler carbon up progressively past 100,000 miles, and what owners describe is a rough idle, lazy throttle response, a check engine light and visible carbon in the intake. Next is the oil. Because the engine burns soot out of the particulate filter by injecting fuel late in the cycle, raw fuel reaches the cylinder walls and some of it drains into the crankcase; the level rises, it smells like diesel and it thins, and over five percent fuel by volume is excessive. Short trips make it worse. The bottom end is honest up to a point: the six-hole spray pattern puts two opposed fuel streams over the wrist pin and creates a hot spot, so cracked pistons turn up around 600 hp or on trucks run with aggressive timing, extra fuel and high towing exhaust temperatures, announced by sudden damage under load and crankcase pressure rather than a slow decline. Head gaskets are the least of it. The riveted design used from late 2006 through 2010 is the best GM fitted and rarely fails on its own; what kills it is an overheat, and then you see coolant loss, a pressurized system and white sweet-smelling smoke.

Stock replacement vs. upgrade

Most Sierra HD owners come to this page for maintenance, and in-kind parts are the right answer there. Let oil analysis set the change interval instead of a number on a sticker, since fuel dilution is what ends the oil on a regenerating engine, and keep a full synthetic low-ash CJ-4 in it. A catch can, serviced regularly, keeps crankcase oil mist out of the intercooler without disturbing the factory closed-crankcase routing. If you are checking a used engine before spending money on it, 300 psi is the minimum compression figure. When the heads are already off a truck that tows or carries a tune, ARP head studs with the riveted-style late-2006-2010 gasket is the rebuild spec, and the A through D grades describe thickness only, so measure and order the grade your engine calls for. Keeping exhaust temperature down and staying off stacked tunes is the cheapest piston insurance there is. Rockers, pushrods and valve springs here are build parts; there is no documented LMM-specific valvetrain failure pattern behind them.

What we carry

Fasteners and build hardware come from ARP and Gator Fasteners, with XDP covering X220 head and main stud kits, connecting rod bolts, crank dowel pin kits, HD rocker arm shafts and billet valve bridges, pushrods, valve springs, harmonic balancers and camshaft and crankshaft position sensors. Pistons are in this group too. Merchant Automotive has the gasket sets a reseal needs, with or without head gaskets and bolts, plus oil cooler installation and seal kits, pushrods, high performance motor mounts, glow plug kits and nuts. Mahle handles rear main crankshaft seals, timing cover gasket sets and seals and lower engine gasket sets. Alliant Power lists head gaskets by grade and side and head installation kits. PPE adds bare cast iron cylinder heads, valve and spring kits, billet pulleys, dual fueler twin pump kits, an oil centrifuge filtration kit and engine mount bushings. Belt drive wear parts are Dayco and Dorman territory, ACDelco covers the PF2232 filter and 9G glow plugs, and oil is Hot Shot's Secret and Lucas Oil in CK-4 grades.

Fitment notes

These pages cover the Sierra 2500HD and the Sierra 3500HD in single and dual rear wheel form, in Work Truck, SLE and SLT trim, across regular, extended and crew cab with the 6 ft 6 in or 8 ft box. Engine parts do not care about the cab, but they care a great deal about the engine code: listings routinely span 2001-2010, 2006-2010 or 2006-2016, which crosses LB7, LLY, LBZ, LMM and LML, so check the code and not just the model year. A 2007 Sierra HD Classic is the earlier body with the LBZ. Chassis cab trucks over 10,000 lb GVWR carried a lower rating than the 365 hp and 660 lb-ft pickup calibration. For 2011 GM reframed these trucks and replaced the LMM with the LML, which runs a CP4 pump and DEF, so do not carry 2010 parts across that line. Use the fitment checker on the product page or call us with the VIN.

Frequently asked questions

My Sierra 2500HD idles rough and feels soft off the line. Where do I start?

Look at carbon first. On an LMM the EGR valve and cooler load up with soot as the miles go on, and that shows up exactly that way: unstable idle, slow throttle response, often a check engine light and visible carbon in the intake tract. It builds progressively, so it is usually a cleanup and inspection job rather than a single failed part.

Do the A, B and C head gasket grades mean better or worse?

Neither. The grades denote thickness, nothing else, and they are chosen to match the deck and head you have in front of you. Gaskets are also sold by side, left and right, so a full set means the correct grade on both banks. Measure before you order, and if the truck tows or is tuned, put ARP studs in while the heads are off.

Will parts for my 2010 Sierra 3500HD fit a 2011?

Often not. For 2011 GM moved the heavy-duty trucks to a new fully boxed frame with revised front suspension and rear springs, and swapped the LMM for the LML with its CP4 injection pump and DEF system. Engine internals, emissions hardware and chassis parts all split at that line. Verify by VIN rather than assuming a 2010 listing covers you.

How do I know whether a used LMM is worth rebuilding?

Start with a compression test. The minimum figure for this engine is 300 psi, so a cylinder meaningfully under that tells you where the money has to go before you plan anything else. Pull an oil sample at the same time and read the fuel dilution number, because an engine run on badly diluted oil has bearing wear you cannot see from the outside. Gasket sets, head gaskets by grade and side, and pistons are all here when the numbers say to open it up.

Not sure what fits? Call the shop at the number in the header, or use the fitment checker on any product page. We install everything we sell.